Whether it stores it on a local server at the ISP or not, you are still wasting your money. Thats what a browser cache is for, technically does the same thing, right?
Netzero and Juno have to be the WORST ISP's ever. They disconnect you every three hours, idle or not. They have annoying software (web toolbar that can't be closed). I haven't tried CTRL ALT DEL'ing out of the software, I would imagine that would disconnect you. And if it didn't, they can tell if you have the software running or not. They will E-Mail you and tell you if they catch you online without their software again, then they will cancel your account.
I would stick with an ISP such as what you have, that you connect through Windows DUN. Much less of a hassle.